This invention relates to torsion spring counter balancing mechanisms for compensating the weight of roll-up doors and a method and structure for accommodating coil torsion spring growth as the door moves up and down between its open and closed positions.
Counterbalancing mechanisms of overhead garage doors utilize coil springs that are placed under a rotational or torsion force to apply a lifting force to the door. The springs are concentrically positioned about a shaft rotatably mounted on fixed supports. The shaft carries hubs accommodating cables. The cables are attached to the door so that when the hubs are rotated, a lifting force will be applied to the door. The lifting force is transmitted to the hubs via the shaft by the torsion springs. The spring must be twisted to load the spring or place the spring under torsion force. Heretofore, long rods have been used to turn the collar attached to the spring to load the spring. This usually requires two men. A limited amount of force can be applied to the spring since twisting the collar is a manual operation. The procedure requires a considerable amount of time and can be dangerous as the spring is loaded with considerable force. A power tool used to apply torsion forces to the counterbalancing spring of a roll-up door is disclosed by E. Dorma in U.S. Pat. No. 3,979,977. One embodiment of this power tool has a power transmission operated with a portable externally located electric motor. Worm gear power transmission units have been incorporated in door counterbalancing mechanisms. Examples of this type of power transmission unit to wind or twist torsion springs are disclosed by L. C. Votroubek and D. H. Nelson in U.S. Pat. No. 3,921,761. Votroubek and Nelson recognize the danger involved in winding and unwinding a garage door torsion spring and attempt to address this problem. Votroubek utilizes a tool with a self-locking worm drive gear and worm wheel which can be put into place about the torsion shaft to effect a gripping of an end collar for connecting the spring to the torsion shaft. After the collar is gripped, the end collar is released from the shaft for movement along the rotation about the torsion shaft. In Votroubek, the tool is mounted on the torsion shaft and blocked against rotation about the torsion shaft in a manner to allow the tool to move axially of the torsion shaft, as the spring is wound, to accommodate the growth of the spring during winding. In a double spring configuration using the Votroubek tool, the springs would be wound and unwound separately with the tool being used to wind the outer-end of each spring.
While Votroubek""s tool lessens danger, as compared to the conventional use of a lever bar for winding or unwinding a spring, the spring end is still held by a tool which is separate from the hardware of the mechanism and which must be assembled and disassembled to the counterbalancing mechanism for each winding, unwinding or adjustment of a torsion spring. This tool also must be securely blocked against rotation as a whole about the axis of the torsion rod each time a spring end is to be wound or unwound. Further, during the use of the tool, as in the case of using a lever bar, the door being counterbalanced is placed in a locked position until the winding operation has been completed and the freed end cones or members of the spring are re-secured to the torsion shaft. With the door locked, the setting of the proper spring forces in the torsion spring or springs is done with the use of charts and spring characteristic specifications. When working in this manner, it is difficult to achieve the proper counterbalancing forces, as is true of all the present conventional methods known to applicant, for setting the torsion in a torsion counterbalancing mechanism for a garage door.
Conventional torsion springs used in door counterbalance mechanisms have adjacent coils that engage or abut one another when the spring is in its normal unwound resting state. There is no gap between adjacent coils. During the winding process of a torsion coil spring friction forces are generated between adjacent coils of the spring. Coil torsion springs having abutting coils that do not provide for growth and contraction of the spring during the initial winding of the spring and of spring unwinding and winding during raising and lowering of the door. Carper et al in U.S. Pat. No. 5,632,063 uses a sliding cone to anchor an end of the torsion spring to the shaft to allow the spring to elongate and contract as the door opens and closes. This requires a modification of the end cone and rod as the cone must axially move on the rod. Conventional shafts and end cones for the torsional coil spring cannot be used in this door counterbalancing system.
It is the object of the present invention to eliminate the dangers of prior art mechanisms relating to torsion spring counterbalancing and to simplify the installation and maintenance with an accompanying savings in time and labor, and to improve the system performance and provide an extended life for the parts of the counterbalance mechanism.
The invention is a method and apparatus for counterbalancing a roll-up door with a coil spring. The spring is located around a shaft operatively connected to the door for transmitting forces between the door and shaft to allow the spring to counterbalance the weight of the door. The spring is elongated to separate adjacent coils before the spring is wound to apply torsion forces to the counterbalancing shaft. The elongated spring allows for spring growth during the winding of the spring. A power transmission, such as a worm gear box, operated with an external tool, such as an electric hand drill, is used to wind the spring.
In one embodiment of the invention, a tubular member located around the shaft and within the spring is used to hold the spring in the elongated position. The spring is normally stretched to the elongated position and attached to the shaft. The power transmission winds the elongated spring to apply torsion force to the shaft. The power transmission also functions to hold the spring in the wound position.
In another embodiment of the invention, a spring stretching assembly surrounding the spring operates to elongate the spring before it is wound to apply torsion force to the counterbalancing shaft. The spring stretching assembly has tubular members threaded together. Rotation of the tubular members relative to each other elongates the spring stretching assembly thereby elongating the spring. The power transmission winds also function to hold the spring in the wound position.
A further embodiment of the invention has a sleeve with a section threaded into a block attached to one end of the spring. The opposite end of the spring is anchored to the counterbalancing shaft. The power transmission, such as a worm gear box, rotates the sleeve relative to the block so as to elongate the spring. A stop member on the sleeve terminates movement of the block. Continued rotation of the sleeve with the power transmission winds the spring to apply torsion force to the shaft. The power transmission retains the spring in the wound position to continuously apply torsion force to the shaft thereby counterbalance the roll-up door.